If people think that not paying (for something they've used), then raising a complaint is the answer then you're in for a shock. It's like me whinging about the cost of the iPhone I bought two years ago, and demanding a partial refund. If people think the ÂŁ500 cost to energy suppliers for going to ombundsman will make the end user better off then they're going to be in for another shock. All they will do is put that cost in the bills, likely into the standing charge. All this will do is inflate the prices to anyone using electricity and gas, or buying things which use electric and gas (which is everything). Then all that will happen is you will get taken to court for what you've used under contract.
It's not the suppliers making most of the money, it's the producers, and then also the government in tax etc.
Just because your contract is with the energy suppliers, does not mean that you going after them will do any good.
Now, there is a thought that if you go after the suppliers, then they will put pressure on the producers, but they won't, largely as they can't as it's an open market.
Assuming we can't increase supply, the only way to get cost down (across the board) is to make demand less, now you can do this by using energy and then not paying, as you will get cut off, and then there will be less people using energy. It won't benefit those who don't pay though, as they won't get connected again until they do pay, and will get chased for what is outstanding. Then you will get a worse credit rating and end up paying higher rates on mortgage, car loans etc.
The basic semi-solution is to just use less, as in have the heating lower, shower on for shorter time, use energy saving products etc. The people won't do this though, as it's a collective action. You will still get the selfish/ ignorant/ rich folk running their heating set on 25 degrees, with the windows open and having two baths a day, full to the brim. They probably don't even notice the energy bill, so won't give a toss.
Rather than going after energy suppliers, you should be aiming the fight at the energy producers or at getting more government support for those who need it most (which may be yourself), and remember things like this when it comes to the next election. Only the government have the power to do something which would significantly help those who need it most. But, pay attention as all you're going to see happen is them apply help across the board which will always massively favour those who need it least, and not give enough to those who need it most.